706 EXTERNAL ANATOMY OF INSECTS. 
guishable. Nothing very remarkable is exhibited by the 
other segments, except that in Trichius the penultimate 
is the largest; in some Staphylinide (Philonthus splen- 
dens) and Brachini (B. melanocephalus) it is emarginate, 
and in the former tribe also often terminating in a white 
membrane. The dorsal segment most worthy of notice 
is the last, which is called the podex ; for though in ge- 
neral it is a minute piece, often retracted within the ab- 
domen and invisible, as in many Diptera, yet sometimes 
it is the most conspicuous of the dorsal segments. It 
is most commonly triangular, and usually deflexed and 
forming an angle with a horizontal line; but in Clythra, 
Chlamys, and Oryctes, it is inflexed; in many Petalocera 
it is nearly vertical. In Cicada, many other Homopte- 
rous Hemiptera, and some Hymenoptera (Cimbez), its 
sides turn down and become ventral; on its lower side 
it has in these a longitudinal cavity which receives the 
ovipositor in repose*. In many other insects it unites 
with the last ventral segment, the hypopygium, to form 
a tube for that organ, as you will find in Callidium vio- 
laceum’, many Muscide, and Thelyphonus. As to its 
termination the podex is sometimes bifid, Blatta ; bipar- 
tite, Ranatra ; mucronate, Szrex ; acuminate, Melolon-. 
tha vulgaris, Acanthurus hemipterus*. Generally this part 
is flat; but the disk is elevated or gibbous in Oryctes and 
some other Lamellicorns. In the majority of the Coleo- 
ptera Order it is quite covered by the wings and ely- 
tra; but in many of the last-mentioned tribe, and some- 
times the penultimate segment also, it is not covered by 
* Reaum. v. é¢. xvii. f. 14. a, a. 
* Linn. Trans. v. t. xii. f. 15. 
© Zool. Journ. No, x. 155. 
